// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_GFX_SEQUENTIAL_ID_GENERATOR_H_
#define UI_GFX_SEQUENTIAL_ID_GENERATOR_H_

#include <stdint.h>

#include <map>

#include "base/containers/hash_tables.h"
#include "base/macros.h"
#include "ui/gfx/gfx_export.h"

namespace ui {

// This is used to generate a series of sequential ID numbers in a way that a
// new ID is always the lowest possible ID in the sequence.
class GFX_EXPORT SequentialIDGenerator {
public:
    // Creates a new generator with the specified lower bound for the IDs.
    explicit SequentialIDGenerator(uint32_t min_id);
    ~SequentialIDGenerator();

    // Generates a unique ID to represent |number|. The generated ID is the
    // smallest available ID greater than or equal to the |min_id| specified
    // during creation of the generator.
    uint32_t GetGeneratedID(uint32_t number);

    // Checks to see if the generator currently has a unique ID generated for
    // |number|.
    bool HasGeneratedIDFor(uint32_t number) const;

    // Removes the generated ID |id| from the internal mapping. Since the ID is
    // no longer mapped to any number, subsequent calls to |GetGeneratedID()| can
    // use this ID.
    void ReleaseGeneratedID(uint32_t id);

    // Removes the ID previously generated for |number| by calling
    // |GetGeneratedID()|.
    void ReleaseNumber(uint32_t number);

    void ResetForTest();

private:
    typedef base::hash_map<uint32_t, uint32_t> IDMap;

    uint32_t GetNextAvailableID();

    void UpdateNextAvailableIDAfterRelease(uint32_t id);

    IDMap number_to_id_;
    IDMap id_to_number_;

    const uint32_t min_id_;
    uint32_t min_available_id_;

    DISALLOW_COPY_AND_ASSIGN(SequentialIDGenerator);
};

} // namespace ui

#endif // UI_GFX_SEQUENTIAL_ID_GENERATOR_H_
